title: A modified Hargreaves' method for assessing threshold temperatures for heat nociception.
abstract: This study describes a modified Hargreaves' method for assessing paw withdrawal threshold temperatures for heat (PWT-H) nociception in the hind paws of rats. This method utilises radiant heat to maintain controlled lamp temperatures (CLTs) on a glass floor beneath the rat hind paw. An ascending series of CLTs were applied for 10s, with 5-10min intervals between applications, until characteristic withdrawal behaviour was observed or a cutoff CLT was reached. The average plantar epicutaneous temperatures measured from anaesthetised rats corresponding to CLTs and withdrawal latencies were used for determining PWT-H. The mean PWT-H in 2-month-old (mo) naïve Sprague-Dawley rats (n=38) was 47.6±0.2°C, which is comparable to the noxious threshold temperature for human glabrous skin (46.5±0.5°C). The PWT-H was consistent between trials and daily assessments over four consecutive days. No significant differences were observed between the PWT-H in 2-, 6- to 8-, and >24-mo F344 rats, but the PWT-H in 1-mo rats was significantly reduced. Three hours following plantar incision, the PWT-H decreased to 37.5±0.2°C, consistent with previous observations of C-fibre afferents from incised glabrous skin firing at 36.7±3.6°C. Parallel testing, using the current method and an electronic von Frey device, illustrated similar degrees of incision-induced hyperalgesia, gradual improvements in hyperalgesia, and reversals induced through morphine and gabapentin. In conclusion, the present method facilitates a comparison of PWT-H using electrophysiological and human psychophysical studies involving thermosensation, and as a behavioural assay identical to von Frey testing, this method also measures the threshold for nociception.
authors.affiliation: Department of Developmental Neurobiology, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA. talktoratan@gmail.com
authors.forename: Ratan K
authors.initials: RK
authors.lastname: Banik
authors.forename: Rajiv A
authors.initials: RA
authors.lastname: Kabadi
mesh_terms: D000375:Aging / Q000502:physiology; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D003627:Data Interpretation, Statistical; D025461:Feedback, Physiological / Q000502:physiology; D005528:Foot / Q000294:innervation / Q000502:physiology; D006358:Hot Temperature; D006930:Hyperalgesia / Q000503:physiopathology; D008297:Male; D059225:Nociception / Q000187:drug effects / Q000502:physiology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D010812:Physical Stimulation; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D012684:Sensory Thresholds / Q000187:drug effects / Q000502:physiology*; D012867:Skin / Q000294:innervation; D013697:Thermosensing / Q000187:drug effects / Q000502:physiology*
chemical_list: D000700:Analgesics
keywords: Gabapentin; Morphine; Nociception; Radiant heat; Rat; Threshold temperature